X-rays are electromagnetic waves excellent in transmittance through an object and are often used for a nondestructive and noncontact observation of the internal structure of an object. An X-ray tube usually makes electrons that have been emitted from an electron gun incident into a target to generate X-rays. For the X-ray tube, as described in Patent Document 1, an electron gun is attached to a tubular member that houses a target to be an anode. Electrons emitted from the electron gun are made incident into the target, and X-rays are generated from the target. The X-rays are transmitted through an X-ray exit window provided on a tube axis of the tubular member housing the target and are irradiated onto an external sample. The X-rays transmitted through the sample are taken as an enlarged perspective image by various X-ray imaging devices.
Patent Document 1: Specification of U.S. Pat. No. 5,077,771